This invention relates to apparatus and a method for analyzing a waveform and in particular to apparatus and method for the statistical eye diagram measurement of a high speed binary pulse coded bit stream.
High-speed communication systems typically communicate with each other by sending serial bit streams of data between transmitters and receivers. These bit streams are usually binary coded pulse signals represented by zeros and ones which may be electrical voltages or optical signals derived from the electrical voltages created by the transmitters and which pulse coded signals are applied to a transmission facility connecting the transmitters with the receivers. The receivers decode the received pulse code signal data to obtain the information therein.
If a receiver receives pulse code signals that have been deformed by errors occurring in the transmission facility problems or if the receiver improperly decodes the received pulse coded signals, the effect is that bit errors may occur in the communications there resulting in wrong information being received by the receiver. Thus, designers, engineers, installers and maintenance personal need to evaluate the stream of pulse coded signals, oftentimes called bit streams, to monitor system performance and to help in diagnosing system problems. It is typical to monitor the quality of such bit streams by using a sampling oscilloscope.
In the monitoring operation, the bit stream and a trigger input in the form of a clock signal having a repetition rate identical to the repetition rate of the bit stream and synchronous therewith are applied to the inputs of the sampling oscilloscope. Samples of the voltage levels of the binary pulses of the bit stream are taken at various time offsets from the repetitive trigger input and are plotted as sample points on the display of the oscilloscope. Voltage samples are continuously taken of the bit stream and added to the sample oscilloscope in combination with the older sample points, which continue to exist on the sample oscilloscope display. Over a relatively short period of time, hundreds or thousands of the sample points on the sample oscilloscope display plot the possible voltage distributions at each time offset from the trigger input. By sweeping all time offsets in the range of interest, a diagram appears on the sampling oscilloscope display, which reveals the quality of the measured high-speed bit stream. This type of diagram, oftentimes called an xe2x80x9ceyexe2x80x9d diagram, is often used to view high-speed binary pulse bit streams during the various development, installation and maintenance phases of high-speed communications systems.
A problem exists in using sampling oscilloscopes in this manner to measure the quality of high-speed communication systems. As the bit stream data rate increases, the bandwidth of the sampling oscilloscopes needed to create the eye diagrams increases proportionally thereto resulting in a higher cost. Another problem arises in that as the cost of the sampling oscilloscopes increases and due to the design issues of super high-speed systems, the present sampling methods takes samples at a relatively few of all the possible edges of the bit stream pulses thereby limiting the current effective sampling rate in the range of ten thousand samples per second by typical known systems. Accordingly, a need exists in the art for an apparatus and a method for actively determining the quality of high-speed binary pulse bit streams used to transfer information and data between communications systems.
It is an object of the invention to provide binary pulse coded waveform measuring apparatus for determining the characteristics of a high speed bit stream of binary pulses used to transfer information between communications systems and in particular to generate an eye diagram defining the quality of the binary pulse bit stream.
It is also an object of the invention to provide to provide logic apparatus for sampling pulse voltage levels in excess of a series of voltage threshold levels during each of a series of delayed clock pulses for a series of pulses of the binary pulse bit stream.
It is also an object of the invention to provide a control apparatus coupled to the logic apparatus and controlled by a programmed processor to generate the series of threshold voltage levels and the delayed clock pulses during each period of a bit stream pulse. The control apparatus accumulates multiple counts of the sampled pulse voltage levels during each delayed clock pulse for a series of pulses of the binary coded pulse bit stream and processes the accumulated counts to generate an eye diagram therefrom defining the characteristics of the binary pulse bit stream.
It is a further object of the invention to provide a method for determining characteristics of a bit stream of binary pulses by sampling pulse voltage levels in excess of voltage threshold levels during each of delayed clock pulses for a series of pulses of the binary coded pulse bit stream. The method generates a series of the voltage threshold levels and the delayed clock pulses during each period of a bit stream pulse and accumulating multiple counts of the sampled pulse voltage levels during each delayed clock pulse for a series of pulses of the binary pulse bit stream. The accumulated counts are processed to generate an eye diagram defining the characteristics of the binary pulse bit stream.
In a preferred embodiment of the invention, apparatus for determining characteristics of a bit stream of binary pulses has measuring apparatus for sampling pulse voltage levels in excess of voltage threshold levels during each of delayed clock pulses for a series of pulses of the binary coded pulse bit stream. Control means coupled to the measuring apparatus generates a series of the threshold voltage levels and the delayed clock pulses during each period of a bit stream pulse and accumulates multiple counts of the sampled pulse voltage levels during each delayed clock pulse for a series of pulses of the binary coded pulse bit stream. The accumulated counts are processed to generate an eye diagram therefrom defining the characteristics of the binary pulse bit stream.
Also in accordance with the preferred embodiment of the invention, a method for determining characteristics of a bit stream of binary pulses generates a series of threshold voltage levels and delayed clock pulses during each period of a bit stream pulse. The method measures and accumulates multiple counts of pulse voltage levels in excess of the generated voltage threshold levels during each delayed clock pulse for a series of pulses of the binary coded pulse bit stream. The method then analyzes the accumulated voltage counts and generates an eye diagram therefrom defining the characteristics of the binary pulse bit stream.